This invention relates to a rotary control valve assembly for controlling operation of a servomotor in an auxiliary power steering system for an automotive vehicle, and more particularly to an improvement to the control valve assembly disclosed in my prior copending application Ser. No. 825,477, filed Aug. 17, 1977, abandoned in favor of continuation application, Ser. No. 37,031, filed May 8, 1979, now U.S. Pat. No. 4,232,586.
According to my prior copending application, a pressure medium control system is disclosed having a rotary plug valve which is journaled at its opposite axial ends by anti-friction bearings mounted in an associated control bushing. In this manner, precise response and perfect functioning is assured since hydraulic jamming of the rotary plug valve and an uncontrolled increase in friction caused thereby, is reliably avoided. The objective of the present invention is to further improve the operational behavior of said pressure medium control system.
Generally, control valve edges on the valve lands formed between the longitudinal passage grooves on a rotary plug valve, are arranged symmetrically on the periphery of the valve element and may be provided with phase control bevels. Such an arrangement is disclosed, for example, in German Pat. No. 1,181,077, column 4, lines 54-55 and in U.S. Pat. No. 4,063,490 to Duffy. The objective associated with such arrangements is to obtain a symmetrical distribution of equal fluid flow forces in order to avoid any resultant transverse force and development of friction therefrom on the rotary plug valve surfaces. Such control bevels are advantageous for regulating pressure that is switched on and off.